Temperature compensated three-port stripline circulator



June 24, 1969 c ANDR|K|AN 3,452,298

TEMPERATURE COMPENSATED THREE-PORT STRIPLINE CIRCULATOR Filed Oct. 17,1967 GYROMAGNETIC MATERIAL x 26 I6 22 I8 22 \-TEMPERATURE COMPENSATINGG'YROMAGNETIC MATERIAL COMPENSATING MATERIAL FIG. 3

. INVENTOR CHARLES F. ANDRIKIAN 0 l l I I l I 6 -80 -40 0 40 80 I20 I60200 240 BY M M 1, 2 J mu ATTORNEYS United States Patent US. Cl. 333-11 2Claims ABSTRACT OF THE DISCLOSURE A stripline ferrite microwavecirculator is temperature compensated over a limited temperature rangeby using two gyromagnetic materials in the place of the normally usedsingle materiaLThe second material is used only for temperaturecompensation and is placed at the RF zero location of the circulator tohave minimum effect on the radio energy. The relative magneticcharacteristics are such that with an increase in temperature a greaterpercentage of the total externally applied flux is passed through themain gyromagnetic material.

Background of the invention In ferrite microwave devices, performancecharacteristics such as isolation. VSWR and insertion loss are affectedby temperature conditions. Such changes in performance characteristicsare due to the decrease in magnetization of both the magnets andmicrowave garnets with an increase in temperature. One prior art schemeto minimize temperature effects is to place a shunt compensation elementoutside of the circulator to then variably shunt the flux from a Cmagnet. This scheme results in a relatively large and heavy packageunsuitable for applications in which minimum weight is of importance,such as spacecraft.

It has been observed that if the externally applied magnetomotive force(H is increased along with the increase in temperature the isolationd.b. will remain substantially constant. This can be accompished withoutincreasing over all device size by placing a magnetic compensatingmaterial within the circulator body in shunt with the external magnets.However, it is necessary that the compensating material have minimummicrowave disturbance.

Summary of the invention In accordance with the present invention thecirculator has its gyromagnetic material divided into two parts,referred to hereinafter as the main or regular gyromagnetic material andthe compensating gyromagnetic material. The main gyromagnetic materialis selected in accordance with known selection criteria to result in acirculator having the desired microwave characteristics. Thecompensating gyromagnetic material is selected to have microwavecharacteristics such as line width (AH), dielectric constant and losstangent as near as possible to the main gyromagnetic material while atthe same time having a greater magnetic saturation over the temperaturerange of interest and a greater slope of magnetic saturation versustemperature over the temperature range of interest. The compensationmaterial is at the center of the circulator where it will cause theleast amount of disturbance to the microwave energy because the RF fieldat the center is zero. At any given temperature the external flux willbe applied in part to the main material and in part to the compensatingmaterial. As the temperature goes up, thereby decreasing the M of thecompensating material by an amount greater than the decrease in M of themain material, a greater portion of the external flux will pass throughthe main material thereby offsetting the temperature eifect on theisolation characteristic.

3,452,298 Patented June 24, 1969 ICC FIGURE 3 shows a graph of magneticsaturation (M versus temperature for two materials useful in the presentinvention.

Although the specific embodiment will be described in connection withone particular geometry of a circulator it will be apparent to anyonehaving ordinary skill in the art that the invention is not confined tothe geometry of the circulator or the specific materials described.

The drawings show a three port stripline ferrite microwave circulatorincluding upper and lower common or ground planes 12 and a cylindricalenclosing wall 14. The circulator is divided into upper and lowerportions by a flat conductor 26 shaped as illustrated. Each of the threearms of conductor 26 are connected respectively to one of the three portconnectors 10. I

The upper portion of the circulator includes a disc shaped gyromagneticmaterial 20 surrounded by a ring shaped dielectric material 24. Thelower portion, identical to the upper portion, includes a disc shapedgyromagnetic material 18 surrounded by ring shaped dielectric material22. Disc magnets 16 are placed on the upper and lower ground plates todirect magnetic flux through the circulator.

The theory and operation of the device described thus far is well knownand therefore need not be discussed herein. The particular dielectricmaterials 22 and 24 and gyromagnetic materials 28 and 20 are those whichwould be encountered in the design of conventional circulators withouttemperature compensation, and the specific types do not form a part ofthe present invention.

In accordance with the present invention a shunt compensatinggyromagnetic material 30 is placed in a hole drilled in the maingyromagnetic material at the center of the circulator. As thetemperature increases the relative magnetic saturations of thecompensation material 30 and main material 18, 20 decreases, causing agreater amount of flux from disc magnets 16 to be applied to the maingyromagnetic material 18, 20. As shown in the drawing. the compensatingmaterial 30 extends from upper ground plane 12 to lower ground plane 12through a hole in the fiat conductor 26. It is not necessary that thecompensating material pass through the conductor 26 but may be placed onopposite sides of the conductor 26 in the same manner as the maingyromagnetic material 18, 20. Also, the compensating material 30 mayextend through holes in the upper and lower plates to come into physicalcontact with the upper and lower disc magnets.

As stated above, the temperature compensating material is a gyromagneticmaterial. Many gyromagnetic materials and their characteristics are Wellknown in the art and the particular one used as the compensating elementis a matter of choice based upon the particular main material used andthe desired temperature range of operation. There are two determiningcriteria in selection of the compensating material:

(1) The saturation magnetization (M of the compensating material must begreater than that of the microwave ferromagnetic material over thetemperature range of operation; and

(2) The change in saturation magnetization with respect to temperatureover the temperature range of operation must be greater for thecompensating material than for the microwave ferromagnetic material.

It is well known that the saturation magnetization or saturation momentof a ferrite or garnet can be lowered by aluminum substitution methods,the methods of substitution also being well known. The more thesubstitution of the aluminum ion in the ferrite or garnet, the lower theresulting saturation magnetization.

As a specific example of materials and saturation magnetizations whichare suitable in the present invention, an unmodified yttrium iron garnethaving a known saturation magnetization of 1780 gauss may be modified bythe substitution of aluminum to form a first modified garnet havingsaturation magnetization of 680 gauss at room temperature and a secondmodified garnet having a saturation magnetization of 1000 gauss at roomtemperature. The method of substitution for lowering the saturationmagnetization is Well known in the art. The former may be used as themain gyromagnetic material and the latter may be the compensatinggyromagnetic material.

The above mentioned main material may be obtained from MicrowaveChemical Labs as their product number MC 1116 PH, and the abovementioned compensating material may be obtained from Trans TechCorporation as their product number G-1010. The curves of magneticsaturation (in gauss) versus temperature C.) for the two materials ofthe specific example are shown in FIG. 3.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is: t

1. In a microwave stripline circulator of the type comprising aplurality of strip-line arms radiating from a common junction region andhaving gyromagnetic material at said junction region adapted to bemagnetized by a direct current magnetic field, the improvementcomprising: dividing said gyromagnetic material into a main material anda compensating material, said compensating material being locatedsubstantially at the center of said junction region and surrounded bysaid main material, said compensating material having a greater magneticsaturation and a greater slope of magnetic saturation versus temperaturethan said main material over the tem- 4 perature range of desiredoperation so as to temperature compensate said circulator.

2. A circulator as claimed in claim 1 wherein said compensating materialand said main material are yttrium iron garnets with aluminumsubstitution.

References Cited UNITED STATES PATENTS 3,174,116 3/1965 5hr 3331.13,246,262 4/1966 Wichert 3331.1 3,273,082 9/1966 Chiron 33324.1 X

HERMANN KARL SAALBACH, Primary Examiner. P. L. GENSLER, AssistantExaminer.

U.S. Cl. X.R.

